1. Field of the Invention
The present invention relates to a multifiber optical connector plug to be connected with another multifiber optical connector plug, so as to connect a pair of multifiber optical cores.
2. Description of the Background Art
A first example of a conventionally known multifiber optical connector plug is shown in FIG. 1, in which a connector plug member 3 houses a plurality of transversely arranged optical fibers 2 projecting out of the end of an optical fiber ribbon 1 and has a pair of guide pin insertion holes 4 with the transversely arranged optical fibers 2 located therebetween, while a connecting facet 5 of the connector plug member 3 has a flat surface perpendicular to the optical axes of the optical fibers 2, where the perpendicular flat surface of the connecting facet 5 has been obtained by the application of a perpendicular polishing. This multifiber optical connector plug of FIG. 1 also includes a clamp spring member 7 for clamping one connector plug member 3 and another connector plug member 3' together when they are connected together.
As shown in FIG. 2, in connecting two multifiber optical cores, the connecting facet 5 of one connector plug member 3 is brought face to face with a connecting facet 5' of another connector plug member 3', with the alignment of the connector plug member 3 and 3' provided by guide pins 6 inserted into the guide pin insertion holes 4 and 4' of the connector plug members 3 and 3'. The connector plug members 3 and 3' are then pressed against each other in an axial direction by attaching the clamp spring member 7 so as to maintain the connected state with a proper alignment.
Here, however, the connecting facets 5 and 5' of the connector plug members 3 and 3' have the microscopic angular errors produced in the perpendicular polishing process, so that there is an air clearance between the connecting facets 5 and 5' when the connector plug members 3 and 3' are connected together straightforwardly. Such a clearance between the connecting facets 5 and 5' could cause the Fresnel reflection of the light beams transmitted through the optical fibers, which in turn causes the deterioration of the emission characteristic of the light source due to the light beams reflected toward the light source, as well as the increase of the connection loss due to the presence of the Fresnel reflection.
For this reason, as shown in FIG. 2, the formation of the clearance between the connecting facets 5 and 5' has been prevented conventionally, by applying a refractive index matching material 8 such as a silicone grease on the connecting facets 5 and 5' before the connecting facets 5 and 5' are brought into contact, so that the refractive index matching material 8 can fill in the clearance between the connecting facets 5 and 5' when the connector plug members 3 and 3' are connected together.
However, this type of a conventional multifiber optical connector plug has been associated with the problems that the tedious and time consuming work of the cleaning of the connecting facets 5 and 5' and the application of the refractive index matching material 7 onto the connecting facets 5 and 5' are required at a time of reconnection or switching.
Also, this configuration of FIG. 2 has been associated with the problem that the angular displacement between the connector plug members 3 and 3' is easily caused by a large impact applied to the assembled connector plug members 3 and 3' such as the impact due to the dropping of the connector, and this angular displacement significantly affects the connection loss of the connector.
A second example of a conventionally known multifiber optical connector plug is shown in FIG. 3, in which a connector plug member 9 houses a plurality of transversely arranged optical fibers 2 projecting out of the end of an optical fiber ribbon 1 and has a pair of guide pin insertion holes 10 with the transversely arranged optical fibers 2 located therebetween, while a connecting facet 11 of the connector plug member 3 has a protruded portion 12 provided at a region surrounding the transversely arranged optical fibers 2, where the protruded protion 12 has a flat end surface 13 perpendicular to the optical axes of the optical fibers 2, which has been obtained by the application of a perpendicular polishing. This multifiber optical connector plug of FIG. 3 also includes a clamp spring member 7 for clamping one connector plug member 9 and another connector plug member 9' together when they are connected together. In this configuration, the connector plug member 9 is usually formed by a plastic material.
As shown in FIG. 4, in connecting two multifiber optical cores, the flat end surface 13 of the protruded portion 12 of one connector plug member 9 is brought face to face with a flat end surface 13' of the protruded portion 12' of another connector plug member 9', with the alignment of the connector plug members 9 and 9' provided by the guide pins 6 inserted into the guide pin insertion holes 10 and 10' of the connector plug members 9 and 9'. The connector plug members 9 and 9' are then pressed against each other in an axial direction by attaching the clamp spring member 7 so as to maintain the connected state with a proper alignment.
In this configuration of FIG. 3, because the protruded portion 12 has the flat end surface 13 which has an area smaller than that of the entire connecting facet 11, the angular errors produced in the perpendicular polishing process can be made substantially smaller compared with the configuration of FIG. 1 described above, and in addition the elastic plastic material is used for for the connector plug members 9 and 9', so that it becomes possible to obtain the direct contact between the endfaces of the optical fibers 2, without using the refractive index matching material.
Here, however, each of the endfaces of the optical fibers 2 is covered by a high refractive index layer of a microscopic scale which is produced as a by-product of the polishing process. As a result, a part of the light beams transmitted through the optical fibers 2 is reflected toward the light source, and for this reason the reflection is limited to a range of approximately -40 to -35 dB, so that it is not applicable to an analog optical transmission system which requires a low reflection characteristic of a reflection below -50 dB.
Moreover, the configuration of FIG. 4 has been associated with the problem that the angular displacement between the connector plug members 9 and 9' is easily caused by an external force exerted in a direction of thickness of the connector plug members or in a direction of width of the connector plug members, because the large part of the connecting facet 11 around the guide pin insertion holes 10 in the connector plug member 9 does not make contact with the connecting facet 11' of the mated connector plug member 9'. As a result, the direct contact between the endfaces of the optical fibers 2 could easily be lost by the external force exerted at a time of connection and reconnection, and the clearance could easily be produced between the flat end surfaces 13 and 13' of the protruded portions 12 and 12' of the connector plug members 9 and 9'. For this reason, it has been difficult for this type of a conventional multifiber optical connector plug to achieve the stable reflection characteristic and connection loss.
Also, just as in the configuration of FIG. 2 described above, this configuration of FIG. 4 has been associated with the problem that the angular displacement between the connector plug members 9 and 9' is easily caused by a large impact applied to the assembled connector plug members 9 and 9' such as the impact due to the dropping of the connector, and this angular displacement significantly affects the connection loss of the connector while possibly also producing the clearance between the flat end surfaces 13 and 13' which causes the Fresnel reflection.
Now, it is noted that the problems described above for the multifiber optical connector plug are equally pertinent to a single fiber optical connector plug, so that a clearance formed between the connecting facets of the connector plug members in a connected state could cause the Fresnel reflection of the light beams transmitted through the optical fibers, and this in turn causes the deterioration of the emission characteristic of the light source due to the light beams reflected toward the light source, as well as the increase of the connection loss due to the presence of the reflected light beams. In a case of a single fiber optical connector plug, this problem has been coped by the following conventionally known configurations.
A first example of a conventionally known single fiber optical connector plug is shown in FIG. 5, in which a connector plug member 16 in a substantially cylindrical shape houses an optical fiber 15 projecting out of the end of an optical fiber cable 14, while a connecting facet 17 of this connector plug member 16 has a convex spherical surface symmetrical with respect to the optical axis of the optical fiber 15, where this spherical surface of the connecting facet 17 has been obtained by the successive application of a perpendicular polishing followed by a spherical polishing using the perpendicularly polished surface as a reference surface. In this configuration, the connector plug member 16 is usually formed by a ceramic material.
As shown in FIG. 5, in connecting two optical fibers, the connecting facet 17 of one connector plug member 16 is inserted into one opening of a guide sleeve 18 and brought face to face with a connecting facet 17' of another connector plug member 16' which is inserted into another opening of the guide sleeve 18, and the connector plug members 16 and 16' are pressed against each other in an axial direction by externally provided springs or other pressing means, such that the alignment of the connector plug members 16 and 16' is achieved by the guide sleeve 18, and a circular contact region is formed on the convex spherical surfaces of the connecting facets 17 and 17'.
The diameter of this circular contact region can be determined from the Young's modulus of the ceramic material used for the connector plug members 16 and 16', the radius of curvature of the spherical surface of the connecting facets 17 and 17', and the force exerted in the axial direction, according to the Hertz formula. As a typical case, when the ceramic material used is an alumina ceramic which has the Young's modulus equal to 370 GPa, the radius of curvature of the spherical surface is 60 mm, and the force exerted in the axial direction is 1 Kgf, the diameter of the circular contact region will be approximately 0.2 mm.
When such a circular contact region is formed, the endfaces of the optical fibers 15 and 15' located at the centers of this circular contact region are put into a direct contact with each other, so that the Fresnel reflection due to the clearance can be eliminated.
However, just as in the configuration of FIG. 3 described above, each of the endfaces of the optical fibers 15 and 15' is covered by a high refractive index layer of a microscopic scale which is produced as a by-product of the polishing process. As a result, a part of the light beams transmitted through the optical fibers 15 and 15' is reflected toward the light source, and for this reason the reflection is limited to a range of approximately -40 to -35 dB, so that it is not applicable to an analog optical transmission system which requires a low reflection characteristic of a reflection below -50 dB.
Moreover, the configuration of FIG. 5 has been associated with the problem that it has been difficult to adapt this configuration for a case of multifiber optical connector plug, because the circular contact region formed at a time of connection is too small to secure the direct contacts for a plurality of optical fibers, and also because it is technically difficult to position a plurality of optical fibers in the cylindrical connector plug member at high accuracy.
A second example of a conventionally known single fiber optical connector plug is shown in FIG. 6, in which a connector plug member 19 in a substantially cylindrical shape houses an optical fiber 15 projecting out of the end of an optical fiber cable 14, while a connecting facet 20 of this connector plug member 19 has an oblique surface which is inclined with respect to the optical axis of the optical fiber 15 by an angle .theta. which is larger than the total reflection critical angle of the light beam transmitted through the optical fiber 15, where this oblique surface of the connecting facet 20 has been obtained by the application of an oblique polishing. In this configuration, the connector plug member 19 is usually formed by a ceramic material.
As shown in FIG. 6, in connecting two optical fibers, the connecting facet 20 of one connector plug member 19 is inserted into one opening of a guide sleeve 18 and brought face to face with a connecting facet 20' of another connector plug member 19' which is inserted into another opening of the guide sleeve 18, such that the alignment of the connector plug members 19 and 19' is achieved by the guide sleeve 18. In this configuration, the endfaces of the optical fibers 15 and 15' make a contact at oblique surfaces inclined at the angle .theta..
Here, however, the connecting facets 20 and 20' of the connector plug members 19 and 19' have a clearance formed therebetween for the following reasons. First, the connecting facets 20 and 20' of the connector plug members 19 and 19' have the microscopic angular errors produced in the oblique polishing process, and these angle errors cannot be absorbed by the relatively hard and less elastic ceramic material from which the connector plug members 19 and 19' are made. Secondly, the angular displacement between the cylindrical connector plug members 19 and 19' can be easily caused in a circumferential direction. Thirdly, the ceramic material from which the connector plug members 19 and 19' are made is harder than the quartz from which the optical fibers 15 and 15' are made, so that the endfaces of the optical fibers 15 and 15' have concave shapes because the optical fibers 15 and 15' are polished by larger extent compared with the connector plug members 19 and 19' at a time of the oblique polishing. Also, just as in the configurations described above, each of the endfaces of the optical fibers 15 and 15' is covered by a high refractive index layer of a microscopic scale which is produced as a by-product of the polishing process.
Nevertheless, because of the contact at oblique surfaces inclined at the angle .theta. which is larger than the total reflection critical angle of the light beams, the reflection due to the clearance formed between the connecting facets 20 and 20' as well as the reflection due to the high refractive index layer are the reflections at the oblique surfaces inclined at the angle .theta., so that the reflected beams are not transmitted toward the light source, and consequently it is possible in this configuration of FIG. 6 to realize the low reflection characteristic of a reflection below -50 dB.
On the other hand, in this configuration of FIG. 6, the presence of the clearance between the connecting facets 20 and 20' could cause the Fresnel reflection of the light beams transmitted through the optical fibers, so that it is still associated with the increase of the connection loss due to the presence of the Fresnel reflection.
Moreover, the configuration of FIG. 6 has been associated with the problem that it has been difficult to adapt this configuration for a case of multifiber optical connector plug, because it is technically difficult to position a plurality of fibers in the cylindrical connector plug member at high accuracy, just as in the configuration of FIG. 5 described above.
There is also a third example of a conventionally known multifiber optical connector plug shown in FIG. 7, in which the feature of the single fiber optical connector plug of FIG. 6 has been adapted for a case of multifiber core. In this configuration of FIG. 7, a connector plug member 21 formed by a silicon material comprises upper and lower halves to be assembled together, where each of the upper and lower halves has a plurality of V shaped grooves formed thereon, and houses a plurality of transversely arranged optical fibers 2 projecting out of the end of an optical fiber ribbon 1 along the V-shaped grooves formed on the upper and lower halves, while a connecting facet 22 of the connector plug member 21 has an oblique surface which is inclined with respect to the optical axis of the optical fibers 2 by an angle .theta. which is larger than the total reflection critical angle of the light beam transmitted through the optical fibers 2, where this oblique surface of the connecting facet 21 has been obtained by the application of an oblique polishing.
As shown in FIG. 8, in connecting two multifiber optical cores, the connecting facet 22 of one connector plug member 21 is inserted into one opening of a guide sleeve 23 and brought face to face with a connecting facet 22' of another connector plug member 21' which is inserted into another opening of the guide sleeve 23, such that the alignment of the connector plug members 21 and 21' is achieved by arc shaped spring members 24 provided inside the guide sleeve 23. In this configuration, the endfaces of the optical fibers 2 and 2' make a contact at oblique surfaces inclined at the angle .theta..
Here, however, the connecting facets 22 and 22' of the connector plug members 21 and 21' have a clearance formed therebetween for the following reasons. First, the connecting facets 22 and 22' of the connector plug members 21 and 21' have the microscopic angular errors produced in the oblique polishing process, and these angular errors cannot be absorbed by the relatively hard and less elastic silicon material from which the connector plug members 21 and 21' are made. Secondly, the silicon material from which the connector plug members 21 and 21' are made is harder than the quartz from which the optical fibers 2 and 2' are made, so that the endfaces of the optical fibers 2 and 2' have concave shapes because the optical fibers 2 and 2' are polished by larger extent compared with the connector plug members 21 and 21' at a time of the oblique polishing. Also, just as in the configurations described above, each of the endfaces of the optical fibers 2 and 2' is covered by a high refractive index layer of a microscopic scale which is produced as a by-product of the polishing process.
In this configuration of FIG. 7, just as in the single fiber optical connector plug of FIG. 6, because of the contact at oblique surfaces inclined at the angle .theta. which is larger than the total reflection critical angle of the light beams, the reflection due to the clearance formed between the connecting facets 22 and 22' as well as the reflection due to the high refractive index layer are the reflections at the oblique surfaces inclined at the angle .theta., so that the reflected beams are not transmitted toward the light source, and consequently it is possible in this configuration of FIG. 7 to realize the low reflection characteristic of a reflection below -50 dB.
On the other hand, in this configuration of FIG. 7, the presence of the clearance between the connecting facets 22 and 22' could cause the Fresnel reflection of the light beams transmitted through the optical fibers, so that it is still associated with the increase of the connection loss due to the presence of the Fresnel reflection.
It is also possible in this configuration of FIG. 7 to apply the refractive index matching material such as a silicone grease on the connecting facets 22 and 22' before the connecting facets 22 and 22' are brought into contact, so that the refractive index matching material can fill in the clearance between the connecting facets 22 and 22' when the connector plug members 21 and 21' are connected together, just as in the configuration of FIG. 1 described above.
However, as already mentioned above, such an application of the refractive index matching material has been associated with the problems that the tedious and time consuming work of the cleaning of the connecting facets 22 and 22' and the application of the refractive index matching material onto the connecting facets 22 and 22' are required at a time of reconnection or switching, so that such an improvement of the connection loss using the refractive index matching material has been applicable only to the very limited circumstances for which very little reconnection or switching operations are required.
There is also an example of a conventionally known multifiber optical connector plug assembly shown in FIG. 9 and FIG. 10, in which the connector plug member similar to that shown in FIG. 1 described above is used as a multifiber connector ferrule 3.
In this configuration of FIGS. 9 and 10, the multifiber optical connector plug assembly comprises: a multifiber connector ferrule 3 housing a plurality of transversely arranged optical fibers 2 projecting out of the end of an optical fiber ribbon 1 and having a pair of guide pin insertion holes 4 with the transversely arranged optical fibers 2 located therebetween; a guide pin stopping member 25 provided behind the multifiber connector ferrule 3 for preventing the guide pins inserted into the guide pin insertion holes 4 from projecting out from the multifiber connector ferrule 3; a spring member 26 provided behind the guide pin stopping member 25 for pressing the multifiber connector ferrule 3 against a mated multifiber connector ferrule in an axial direction; and a front housing 27 and a rear housing 28 for integrally housing the multifiber connector ferrule 3, the guide pin stopping member 25, and the spring member 26 together.
As shown in FIG. 11, in connecting two multifiber optical connector plug assemblies to form a multifiber optical connector, the guide pins 6 are inserted into the guide pin insertion holes 4 of one multifiber optical connector plug assembly A first, and then this multifiber optical connector plug assembly A is inserted into one opening of an adaptor B until hook members 30 provided on the adaptor B are engaged with groove portions 29 formed on the front housing 27 of this multifiber optical connector plug assembly A.
Then, another multifiber optical connector plug assembly A' is inserted into another opening of the adaptor B until the hook members 30' provided on the adaptor B are engaged with groove portions 29' formed on the front housing 27' of this another multifiber optical connector plug assembly A'. Here, the guide pins 6 are also inserted into the guide pin insertion holes 4' of this another multifiber optical connector plug assembly A', such that the alignment of the optical fibers housed inside the multifiber optical connector plug assemblies A and A' is provided by guide pins 6.
In a case of reconnection or switching, the detachment of the multifiber optical connector plug assemblies is achieved by releasing the engagement of the hook members 30 and 30' of the adaptor B with the groove portions 29 and 29' of the multifiber optical connector plug assemblies A and A', and pulling the multifiber optical connector plug assemblies A and A' out of the adaptor B.
Now, in this configuration, the guide pins 6 inserted into the guide pin insertion holes 4 and 4' are commonly provided for both of the multifiber optical connector plug assemblies A and A' and not fixed to either one of the guide pin insertion holes 4 and 4'. For this reason, there has been cases in which the guide pins 6 have dropped off the multifiber optical connector plug assemblies A and A', which severely damaged the maneuverability of this multifiber optical connector plug assembly in the connection and reconnection operations.
It is to be noted here that the fixing of the guide pins 6 to either one of the guide pin insertion holes 4 or 4' by means of adhesive or other fixing means does not solve this problem of the maneuverability just mentioned, because of the following reasons.
First of all, if such a fixing of the guide pins 6 is employed, the multifiber optical connector plug assemblies would have to come into two forms of a male plug assembly having the guide pins 6 fixed and a female plug assembly without the guide pins 6, so that each plug assembly would have a predetermined specific connection orientation, and this can severely limit the wide applicability of the plug assembly in a sense that a given plug assembly is not necessarily be always capable of being connected with another arbitrary plug assembly.
Secondly, if such a fixing of the guide pins 6 is employed, it would be difficult to provide a sufficient cleaning of the endface of the plug assembly required at a time of the connection and reconnection operation, especially for the male plug assembly having the guide pins 6 fixed thereon.